Gallium Nitride (GaN) is proven to be the material of choice for high-frequency, high-power, and high-temperature applications owing to its wide bandgap and large breakdown electric field. GaN also offers a number of excellent mechanical properties such as strong piezoelectric and pyroelectric effects, high acoustic velocity, and superb mechanical and chemical stability, making it a suitable material for nano/microelectromechanical systems (NEMS/MEMS). High-performance GaN micromechanical resonators operating in gigahertz regime are required for a number of applications. Extending the frequency of GaN resonators deep into the gigahertz regime, where GaN ICs usually operate at, is hindered because of a large capacitive feedthrough between the input/output electrodes. In this disclosure, a resonant-body high electron mobility transistor (RB-HEMT) operating in thickness mode is introduced.
The concept of resonant body or resonant gate transistors (RBT's or RGT's) dates back to the introduction of the MEMS resonators. In the past few years, research on RBT's was revived mostly using silicon (Si) as the resonating material. One major difference between GaN RB-HEMTs and Si-based RBTs is the origin and the properties of the transistor conduction channel. Spontaneous and piezoelectric polarization creates a fixed positive charge at the AlGaN/GaN interface. The positive sheet charge confines electrons at the AlGaN/GaN interface in a potential well, forming a 2-D electron gas (2-DEG) channel present at a zero gate voltage (i.e., the transistor is normally ON). The origin of the conduction channel in the III-nitride HEMT structures suggests that these transistors are very sensitive to mechanical stress, which changes the piezoelectric polarization-induced surface and interface charges. In Si-based transistors, however, the conduction channel is based on creating an inversion layer in the doped substrate by applying a gate voltage, which results in a higher scattering due to the presence of parent atoms in the channel, higher 1/f noise, lower channel carrier mobility, and more pronounced electron scattering because of imperfections and surface roughness at the noncrystalline silicon/silicon dioxide interface. Above all, unlike Si-based field effect transistors, GaN HEMTs make it possible to take advantage of piezoelectric actuation inherent in GaN material systems.
An AlGaN/GaN resonant body HEMT was first demonstrated in M. Faucher, et al's “Amplified Piezoelectric Transduction of Nanoscale Motion In Gallium Nitride Electromechanical Resonators”, Appl. Phy. Lett., Vol. 94, No. 23, page 233506, June 2009, and was used to excite the flexural-mode resonance of a beam with frequencies in low megahertz range. In this disclosure, a single resonating HEMT is described that not only is the main vibrating element, but also is used to transduce the thickness-mode acoustic resonance.
This section provides background information related to the present disclosure which is not necessarily prior art.